For manufacturing, science, and technology (MSAT) leaders tasked with ensuring process robustness, driving technology transfer, and supporting lifecycle optimization, connectivity represents something much larger than component compatibility. It is the foundation for standardization, predictability, and control. Every connection influences whether a process can be reliably transferred, consistently executed, and confidently scaled. When done right, early process decisions can translate to accelerated progress across development and scale‑up.
For organizations developing mAbs, mRNA therapies, antibody-drug conjugates (ADCs), multispecific antibodies, and cell therapies—process robustness, technology transfer, and manufacturing scalability increasingly rely on the effectiveness of single-use assemblies. Yet one factor remains consistently underestimated: physical connectivity, or fluid management. The tubing, connectors, sensors, and fluid transfer paths that link unit operations together can have a profound impact on flow behavior, process consistency, scalability, and regulatory compliance.
As therapies become more complex and manufacturing networks expand across sites, every connection point in a process becomes a potential source of variability. These connectors are not merely passive components. Together, they define how material moves through a process, how consistently the process performs, and how easily it can be transferred, replicated, and scaled.
The challenge is that bioprocesses may evolve over time based on modality-specific requirements, which means incorporating new equipment or retrofitting technologies. A straightforward process can then become a patchwork of connection types, tubing dimensions, materials, and supplier specifications. As manufacturers document deviations and are forced to troubleshoot flow inconsistencies and validate component changes, they’re left repeatedly asking the question, Why does this process behave differently here than it did there?
Physical connectivity is not simply about ensuring components fit together, it’s ensuring that the entire manufacturing system functions together. The performance of a process is influenced not just by a connector, tubing segment, or flow kit, but by how all the elements of the fluid pathway interact as an integrated system. Small decisions made upstream can have significant consequences downstream. In this article, we discuss a few examples of why connectors can’t be chosen with only one piece of the process in mind.
End-to-end fluid management: why flow kits can’t be designed in isolation
In modern biomanufacturing, every transfer step must behave as expected. Unexpected flow behavior can result in batch delays, troubleshooting efforts, product loss, or deviations that impact manufacturing efficiency. Yet flow path design decisions are often evaluated at the equipment level rather than at the process level. Because fluids do not recognize equipment boundaries, the performance of a flow kit is influenced by the entire transfer system surrounding it. Designing flow kits in isolation can therefore create hidden risks that are not discovered until the process is operating under real manufacturing conditions.
A common misconception in bioprocessing is that a flow kit can be designed around the requirements of the processing unit alone. The entire fluid transfer pathway within this skid, from the origin through the flow kit and to the destination, must be considered. Take, for example, a chromatography skid with a flow kit designed around a bore size of “X.” In chromatography, bore size refers to the internal diameter (ID) of the tubing. At first glance, it may seem reasonable to use X as the bore size through the system. However, many manufacturing facilities operate with long transfer distances between buffer preparation areas and process skids. Over those distances, pressure losses can become significant.
In these cases, MSAT and process engineers may intentionally specify a bore size larger than X, even though this is larger than the bore of the system flow path itself. The larger tubing diameter helps reduce pressure drop across long runs, minimizing the risk of cavitation, tubing collapse, pump performance issues, and process interruptions.
Cavitation occurs when the local pressure in a fluid falls below the fluid’s vapor pressure, causing vapor bubbles to form, which can collapse violently in high-pressure regions. This can cause unstable flow rates, increased shear stress, and process conditions drifting away from target operating ranges, making the process unpredictable. Predictability means easier technology transfer between sites and easier scale up down the line.
A successful design requires consideration of the entire transfer pathway, including:
- Mixer bag and tote outlet sizes
- Tubing diameters across transfer distances
- Transfer set configurations
- Pump requirements
- Pressure-drop limitations
- Aseptic connector sizing
- Final flow kit geometry
What appears to be a simple tubing selection decision is often a system-level engineering decision. For organizations seeking predictable manufacturing performance, every connection point must be considered within the context of the complete process. A well-designed fluid management strategy accounts not only for the flow kit itself, but also for the entire network of components that deliver fluid to and from the process (Fig 1).
Fig 1. Cytiva’s Batch 360™ service collaborates with you to design a single-use consumable package optimized for your end-to-end manufacturing workflow.
A tubing change that looks small but behaves big
Here, we show changes to ID can multiple the effects on characteristics of fluid and its flow path. If an MSAT team keeps the same target flow rate but reduces tubing ID from 1/2 inch to 1/4 inch, the fluid velocity increases four-fold, the laminar pressure-drop estimate increases sixteen-fold, and wall shear increases eight-fold. That is before accounting for fittings, reducers, bends, pump pulsation, connector geometry, or turbulent effects (Table 1).
Using Hagen-Poiseuille behavior for laminar Newtonian flow, volumetric flow is proportional to the fourth power of tube radius, which is why Harvard’s demonstration notes that 16 smaller tubes are needed to pass as much water as one tube with twice the diameter (1).
If the pressure-driving capability stays the same and the tubing ID is cut in half, Hagen-Poiseuille scaling suggests:
- Flow ratio = (new radius/old radius)4
- Flow ratio = (0.25 in./0.5 in.)4
- Flow ratio = (0.5)4 = 1/16
A line change that halves internal diameter can reduce flow capacity to roughly one-sixteenth under laminar assumptions, or force the system to compensate through higher pressure, longer processing time, different pump settings, or altered process conditions. That is why physical connectivity decisions can become process-performance decisions.
Table 1. How tubing diameter changes affect characteristics of fluid flow
|
Parameter |
1/2 in. (12.70 mm) ID tubing |
1/4 in. (6.35 mm) ID tubing |
What changes |
|
Radius |
6.35 mm |
3.18 mm |
2x smaller |
|
Cross-sectional area |
1.27 cm² |
0.32 cm² |
4x smaller |
|
Average velocity at 1 L/min |
0.13 m/s |
0.53 m/s |
4x higher |
|
Estimated Reynolds number |
~1,671 |
~3,342 |
Moves toward transition |
|
Laminar pressure-drop estimate |
~26 Pa/m |
~418 Pa/m |
16x higher |
| Wall shear estimate | ~0.083 Pa | ~0.663 Pa | 8x higher |
If an MSAT team keeps the same target flow rate but reduces tubing ID from 1/2 inch to 1/4 inch, the impact is far greater than simply making the system "a little more restrictive." The narrower tubing forces the same volume of fluid through a much smaller cross-sectional area, causing fluid velocity to increase significantly. As velocity increases, so do pressure requirements and mechanical stresses within the system.
In practice, this means operators may need to work harder to achieve the desired transfer rate, pumps may experience higher loads, and the process becomes more sensitive to variations throughout the flow path. What appears to be a minor design change can affect overall system performance, particularly when transferring large volumes, operating over long distances, or working with shear-sensitive products. Peer-reviewed work on tubing in parenteral filling lines highlights that protein-based products can be sensitive to interfacial and shear stress, and that scale-down or transfer models should preserve relevant stress exposure when comparing commercial and laboratory scales (2).
Smaller tubing ID also changes extractables and leachables material exposure
Continuing on with our example of cutting ID tubing in half, we show how this can also affect material exposure to extractables and leachables (E&L). For a 1 meter section of tubing, wetted surface area and hold-up volume shift in opposite ways (Table 2).
Table 2. Effects on material exposure parameters related to reduction in tubing ID
|
Parameter |
1/2 in. ID tubing |
1/4 in. ID tubing |
|
Wetted surface area per meter |
~399 cm² |
~199 cm² |
|
Hold-up volume per meter |
~127 mL |
~32 mL |
|
Surface-area-to-volume ratio |
~3.15 cm²/mL |
~6.30 cm²/mL |
The smaller tube has less total contact area per meter, but the fluid inside it sees approximately double the wetted surface area per mL of process fluid. Importantly, E&L risk assessments commonly consider component contact, material of construction, process stream chemistry, temperature, contact duration, surface area, and patient exposure.
If a tubing or connector component has an extractables result of 0.05 µg/cm² for a compound, then a 1 m section of 1/4 in. ID tubing with ~199 cm² wetted surface area gives:
- Potential extractable mass = 0.05 µg/cm² × 199 cm²
- Potential extractable mass = 9.95 µg
If the contacted process volume is 10 L:
- Theoretical concentration = 9.95 µg/10 L
- Theoretical concentration = 0.995 µg/L
- Theoretical concentration = 0.000995 µg/mL
The number may look small, but it is not evaluated in isolation. The relevant question is whether that material, under that process chemistry, temperature, contact time, surface-area-to-volume ratio, downstream clearance profile, and patient-dose assumption is defensible in a regulatory package. In fact, a Parenteral Drug Association (PDA) Journal of Pharmaceutical Science and Technology study on single-use flexible plastic biocontainers identified 53 organic extractable compounds from four commercially available single-use bags, with many described as degradation products of polymer additives; the abstract states that extractables profiling has become essential in qualification of single-use systems for drug manufacturing (3).
Ensuring batch consistency, process robustness, and reproducibility with connected flow paths
For manufacturing teams, the concern is not simply whether fluid can move from point A to point B, but whether it can do so predictably and repeatedly. A flow path that performs differently than expected can complicate scale-up, increase troubleshooting efforts during tech transfer, and reduce confidence that process performance observed during development will be replicated in manufacturing. Evaluating the entire fluid pathway rather than individual components helps identify these risks early, when design changes are less costly and easier to implement.
This is why seemingly small flow-path decisions deserve careful consideration. Changes in tubing diameter, component selection, or flow-path architecture can have cascading effects throughout the system. Taking a holistic approach to fluid management helps ensure that the final design supports robust, scalable, and predictable manufacturing performance rather than introducing hidden constraints that only become apparent during operation.
Reducing process variability across single-use systems fluid management
The key lesson is that fluid dynamics are not linear. Small changes in flow-path design can create outsized impacts on process performance. Understanding those interactions before implementation can help manufacturers avoid costly surprises, accelerate scale-up, and build more robust bioprocesses from development through commercial production.
Many connectivity challenges are not discovered when a component is selected. They are discovered during scale-up, technology transfer, or commercial manufacturing. Cytiva works alongside you to design, evaluate, and optimize manufacturing systems with the goal of reducing complexity, improving standardization, and creating more robust processes from development through commercial production. Visit Cytiva Integrated solutions to find out more about our single use solutions.
References
- Harvard Natural Sciences Lecture Demonstrations. Poiseuille's Law. https://sciencedemonstrations.fas.harvard.edu/presentations/poiseuilles-law. Accessed August 25, 2026.
- Moino C, Scutellà B, Bellini M, Bourlès E, Boccardo G, Pisano R. Analysis of the shear stresses in a filling line of parenteral products: the role of tubing. Processes. 2023;11(3):833. doi:10.3390/pr11030833
- Marghitoiu L, Liu J, Lee H, et al. Extractables analysis of single-use flexible plastic biocontainers. PDA J Pharm Sci Technol. 2015;69(1):49-58. doi:10.5731/pdajpst.2015.01001